FAIR VALUES OF FINANCIAL INSTRUMENTS: (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Fair value measurement
Securities available-for-sale	$ 891,082	$ 897,053
U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	10,693	1,467
Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	213,164	187,936
Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	9	17
Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	437,634	484,655
State and municipal obligations
Fair value measurement
Securities available-for-sale	214,707	207,675
Collateralized debt obligations
Fair value measurement
Securities available-for-sale	14,875	15,303
Level 1
Fair value measurement
Securities available-for-sale	0	0
Level 2
Fair value measurement
Securities available-for-sale	871,482	875,850
Derivative Assets	1,176	1,062
Derivative Liabilities	(1,176)	(1,062)
Level 2 | U.S. Government entity mortgage-backed securities
Fair value measurement
Securities available-for-sale	10,693	1,467
Level 2 | Mortgage-backed securities, residential
Fair value measurement
Securities available-for-sale	213,164	187,936
Level 2 | Mortgage-backed securities, commercial
Fair value measurement
Securities available-for-sale	9	17
Level 2 | Collateralized mortgage obligations
Fair value measurement
Securities available-for-sale	437,634	484,655
Level 2 | State and municipal obligations
Fair value measurement
Securities available-for-sale	209,982	201,775
Level 3
Fair value measurement
Securities available-for-sale	19,600	21,203
Level 3 | State and municipal obligations
Fair value measurement
Securities available-for-sale	4,725	5,900
Level 3 | Collateralized debt obligations
Fair value measurement
Securities available-for-sale	$ 14,875	$ 15,303